Heat-resistant, high-toughness aluminum alloy, method of manufacturing the same, and engine parts

ABSTRACT

This invention provides a heat-resistant, high-toughness aluminum alloy which has a good balance between strength and ductility at a temperature from room temperature to around 300 degrees C. and has a high fracture toughness, a method of manufacturing the same, and engine parts. The heat-resistant, high-toughness aluminum alloy of this invention contains 10 to 16 mass. % of silicon, 1 to 3 mass % of iron, 1 to 2 mass % of nickel, 0.5 to 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, 0.6 to 3 mass % of copper, and 0.2 to 2 mass % of magnesium, the balance being essentially aluminum, and is obtained by densifying aluminum alloy powder prepared by gas atomizing. The silicon has an average grain diameter of 4 μm or less.

TECHNICAL FIELD

The present invention relates to heat-resistant, high-toughness aluminum alloys, methods of manufacturing the same, and engine parts, and particularly to heat-resistant, high-toughness aluminum alloys which are made by rapid solidification and are suitable as materials for automotive engine parts, for which high heat resistance and toughness are required, particularly as materials for pistons.

BACKGROUND ART

Unexamined Japanese patent publication 11-293374 (patent publication 1) discloses heat-resistant, rapidly solidified aluminum alloys of Al (aluminum)—Si (silicon)—transition metal. Specifically, this publication discloses aluminum alloys comprising 10 to 30 mass % of Si, 1 to 5 mass % of Ti (titanium), 3 to 10 mass % in total of at least one of Fe (iron) and Ni (nickel), and 0.05 to 1.0 mass % of Mg (magnesium), the balance being essentially Al, and in which the silicon has an average grain diameter of not more than 2 μm, and the intermetallic compound phase not containing Si has an average grain diameter of not more than 1 μm.

This publication also discloses that the above aluminum alloys are used for e.g. engine parts.

Patent publication 1: Unexamined Japanese patent publication 11-293374

DISCLOSURE OF THE INVENTION Problems to which the Invention Seeks a Solution

The aluminum alloys disclosed in the above patent publication are suitable as materials for e.g. engine parts because they have high heat resistance and high wear resistance. In cases where higher load operation is required for engines, e.g. for car races, besides high strength, high toughness and low specific gravity, lightness in weight and high durability are also required for engine parts, particularly for pistons. Therefore, the need for materials which satisfy these requirements is increasing.

An object of the present invention is to provide heat-resistant, high-toughness aluminum alloys which have a good balance between strength and ductility at a temperature range from room temperature to around 300 degrees C. and have high fracture toughness, a method of manufacturing the same, and engine parts made of such alloys.

Means to Solve the Problems

The heat-resistant, high-toughness aluminum alloy according to the present invention comprises not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum, the alloy being obtained by densifying aluminum alloy powder prepared by gas atomizing, the silicon having an average grain diameter of not more than 4 μm.

Preferably, the heat-resistant, high-toughness aluminum alloy contains titanium by not less than 0.5 mass % and not more than 2 mass %.

Preferably, the heat-resistant, high-toughness aluminum alloy has a density of 2.8 Mg/m³ or less.

The engine parts according to the present invention are manufactured by subjecting any of the abovementioned heat-resistant, high-toughness aluminum alloys to hot plastic working.

The engine parts are preferably pistons.

One method of manufacturing a heat-resistant, high-toughness aluminum alloy according to the present invention comprises preparing aluminum alloy powder by gas atomizing, the aluminum alloy powder comprising not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum, subjecting the aluminum alloy powder to cold forming to obtain a preform, heating the preform to a temperature range of not less than 400 degrees C. and not more than 510 degrees C. and holding the preform in the temperature range for 5 hours or less, and subjecting the preform to hot plastic working to densify the preform, thereby obtaining a dense body as the heat-resistant, high-toughness aluminum alloy, the silicon in the aluminum alloy having an average grain diameter of 4 μm or less.

Another method of manufacturing a heat-resistant, high-toughness aluminum alloy according to the present invention comprises preparing aluminum alloy powder by gas atomizing, the aluminum alloy powder comprising not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum, subjecting the aluminum alloy powder to cold forming to obtain a preform, heating the preform to a temperature range of 400 degrees C. to 510 degrees C. and holding the preform in the temperature range for 5 hours or less, subjecting the preform to hot plastic working to densify the preform, thereby obtaining a dense body, and subjecting the dense body to hot plastic working by heating to a temperature not higher than the heating temperature of the preform, thereby manufacturing the aluminum alloy, the silicon in the aluminum alloy having an average grain diameter of 4 μm or less.

In either of the above methods, the step of subjecting the heated preform to hot plastic working preferably includes extrusion with an extrusion ratio of 6 or more.

Advantages of the Invention

The present inventors have discovered that by preparing aluminum alloy powder of a predetermined composition by gas atomizing and densifying the aluminum alloy powder thus prepared, heat-resistant, high-toughness aluminum alloys can be obtained which have a good balance between strength and ductility at a temperature range from room temperature to around 300 degrees C. and have high fracture toughness. Such aluminum alloys are suitable as materials for automotive engines parts such as pistons.

In the heat-resistant, high-toughness aluminum alloy according to the present invention, silicon is important to improve heat resistance while keeping a low specific gravity. The content of silicon should be not less than 10 mass % and not more than 16 mass % because if the silicon content is less than 10 mass %, the strength at high temperature tends to be low. If over 16 mass %, the elongation and impact value at high temperature tend to be low.

Iron is important to improve heat resistance. The content of iron should be not less than 1 mass % and not more than 3 mass % because if the iron content is less than 1 mass %, the strength at high temperature will be low. If over 3 mass %, the elongation and the impact value at high temperature will be low.

Nickel is important to improve heat resistance. The content of nickel should be not less than 1 mass % and not more than 2 mass % because if the nickel content is less than 1 mass %, the strength at high temperature tends to be low. If over 2 mass %, the elongation and the impact value at high temperature will be low.

One or more of titanium, zirconium, chromium and vanadium is important for densification of the material and to improve the strength by forming an intermetallic compound with aluminum and functioning as a core of crystal formation. The total content of such one or more of titanium, zirconium, chromium and vanadium should be not less than 0.5 mass % and not more than 2 mass % because if it is less than 0.5 mass %, the strength at high temperature and the strength at room temperature will be low, and if over 2 mass %, the elongation and the impact value at high temperature will be low.

Copper is important to improve the strength by ageing precipitation hardening at a temperature range from room temperature to around 200 degrees C. The content of copper should be not less than 0.6 mass % and not more than 3 mass % because if the copper content is less than 0.6 mass %, the strength at high temperature and the strength at room temperature will, and if over 3 mass %, the impact value decreases and the density increases.

Magnesium has an effect similar to copper. The content of magnesium should be not less than 0.2 mass % and not more than 2 mass % because if the magnesium content is less than 0.2 mass %, the strength at room temperature is low, and if over 2 mass %, the impact value and the elongation at room temperature decrease.

Since the heat-resistant, high-toughness aluminum alloys contain titanium, which has a low specific gravity, in the amount of not less than 0.5 mass % and not more than 2 mass %, their specific gravity decreases, and their properties further improve.

By setting the density of the heat-resistant, high-toughness aluminum alloys below 2.8 Mg/m³, it is possible to reduce their specific gravity and thus reduce the weight of parts made therefrom.

Because the engine parts according to the present invention are manufactured by subjecting any of the abovementioned heat-resistant, high-toughness aluminum alloys to hot plastic working, they satisfy the requirements for strength, toughness and low specific gravity and are lightweight and have excellent durability.

By either of the methods of manufacturing heat-resistant, high-toughness aluminum alloys according to the present invention, it is possible to manufacture heat-resistant, high-toughness aluminum alloys which have a good balance between strength and ductility at a temperature range from room temperature to around 300 degrees C. and have high fracture toughness. The dense body is subjected to hot plastic working by heating at a temperature lower than the temperature for heating the preform. It is to prevent the ductility from decreasing.

In the methods of manufacturing heat-resistant, high-toughness aluminum alloys according to the present invention, extrusion is carried out with the extrusion ratio of 6 or more to improve toughness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing a first method of manufacturing the heat-resistant, high-toughness aluminum alloy embodying the present invention;

FIG. 2 is a flow chart showing a second method of manufacturing the heat-resistant, high-toughness aluminum alloy embodying the present invention;

FIG. 3 is a front view of a tensile test specimen;

FIG. 4(a) is a front view of an impact test specimen;

FIG. 4(b) is a sectional view of the same; and

FIG. 4(c) is an enlarged view of a notch.

DESCRIPTION OF NUMERALS

-   1 Tensile test specimen -   2 Impact test specimen -   2 a Notch

BEST MODE FOR EMBODYING THE INVENTION

Now the embodiments of the present invention are described with reference to the drawings.

A heat-resistant, high-toughness aluminum alloy embodying the present invention comprises not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum. The heat-resistant, high-toughness aluminum alloy of this embodiment is obtained by densifying aluminum alloy powder prepared by gas atomizing. The silicon therein has an average grain diameter of not more than 4 μm.

Preferably, the heat-resistant, high-toughness aluminum alloy according to the present invention contains titanium in the amount of not less than 0.5 mass % and not more than 2 mass %. Also, the heat-resistant, high-toughness aluminum alloy of this invention preferably has a density of 2.8 Mg/m³ or less.

Pistons are manufactured by subjecting the heat-resistant, high-toughness aluminum alloy of this invention to hot plastic working.

Next, the methods of manufacturing the heat-resistant high-toughness aluminum alloy embodying this invention are described.

FIG. 1 is a flow chart showing a first method of manufacturing a heat-resistant, high-toughness aluminum alloy embodying the present invention. As shown in FIG. 1, a predetermined molten composition is prepared (Step 1) which comprises not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, and not less than 0.5 mass % and not more than 2 mass % in total of one or more of titanium, zirconium, chromium and vanadium, the balance being essentially aluminum. Preferably, the molten composition contains titanium in the amount of not less than 0.5 mass % and not more than 2 mass %.

The molten composition is air atomized to prepare aluminum alloy powder (Step S2). The aluminum alloy powder is then cold compression molded into a preform (Step S3). The preform is heated to a temperature of not lower than 400 degrees C. and not higher than 510 degrees C. and maintained in this temperature range for 5 hours or less in an atmospheric furnace (Step S4). The heated preform is densified by hot plastic working into a dense body (Step S5). The hot plastic working is preferably extrusion with the extrusion ratio of 6 or more. The dense body is then cut and heated to a temperature lower than the heating temperature of the preform (not lower than 400° C. and not higher than 510° C.) and subjected to hot plastic working (Step S6). The heat-resistant, high-toughness aluminum alloy of this embodiment is thus obtained, the silicon therein having an average grain diameter of not more than 4 μm.

The aluminum alloy thus produced is worked into test specimens (Step S7) which are subjected to material tests (tensile test and Charpy impact test), to be described below (Step S8).

FIG. 2 is a flow chart showing the second method of manufacturing a heat-resistant, high-toughness aluminum alloy embodying the present invention. As shown in FIG. 2, this method is the same as the method of FIG. 1 from Step S1 to Step S5. After Step S5, the dense body densified by extrusion is cut (Step S11), heated (Step S12), subjected to plastic working (swaging) (Step S13) and subjected to heat treatment (Step S14).

Thereafter, in this method, too, as in the method of FIG. 1, the aluminum alloy is worked into test specimens (Step S7), which are subjected to material tests (tensile test and Charpy impact test), to be described below (Step S8).

EXAMPLE 1

Examples of the present invention are now described.

Molten compositions shown in Table 1 were prepared and formed into tensile test specimens and impact test specimens according to the flow of FIG. 1. FIGS. 3 and 4 show a tensile test specimen and an impact test specimen, respectively. FIG. 3 is a front view of the tensile test specimen 1. FIG. 4(a) is a front view of the impact test specimen 2, FIG. 4(b) is its sectional view, and FIG. 4(c) is its enlarged view showing its notch 2 a.

For these test specimens, measurements were made of the average grain diameter of the silicon, tensile strength and elongation at 300 degrees C., tensile strength and elongation at room temperature (20 degrees C.), impact value and density. Table 2 shows the results. Table 2 also shows the solidifying temperature of the preform formed into the respective test specimens, holding time after heating the preform, and extrusion ratio, solution treatment temperature, and artificial ageing temperature for the heated preform. TABLE 1 Specimen Content(mass %) No. Si Fe Ni Ti Cr Zr V Cu Mg Example of  1 10 2 1.3 1.1 — — — 1 0.5 the invention  2 12 2.1 1.6 1.2 — — — 0.9 0.7  3 13 2.1 1.4 0.9 — — — 1.1 0.7  4 15 1.9 1.5 1.6 — — — 1.3 0.6  5 16 2.1 1.4 1.4 — — — 1.4 0.8  6 13 1.1 2.1 1 — — — 1.5 1  7 13 2.8 1.1 1.5 — — — 1.4 0.6  8 13 2.1 1.1 1.3 — — — 1.3 1  9 13 1.2 2.9 1.2 — — — 1 1.1 10 13 2 14 0.5 — — — 1.1 0.5 11 13 1.8 1.3 1.8 — — — 0.9 0.8 12 13 1.8 1.5 — 1.2 — — 0.8 0.6 13 13 1.9 1.6 — — — 1.3 1.1 0.5 14 13 1.8 1.4 — — 1.2 — 1 0.8 15 13 1.9 1.5 1.1 — — — 0.6 0.9 16 13 2 1.3 1 — — — 2.8 1 17 13 1.8 1.5 1 — — — 0.9 0.4 18 13 2.1 1.6 1.3 — — — 1.1 1.5 Comparative 19 8 2.3 1.6 0.9 — — — 1.1 0.5 Example 20 18 2 1.5 1.2 — — — 1.4 0.6 21 13 4 — 1 — — — 1.2 0.8 22 13 — 4.2 1.1 — — — 1.1 0.7 23 13 3 2.8 0.8 — — — 1 1 24 13 0.8 0.5 0.8 — — — 1.2 0.8 25 13 2.2 1.4 2.2 — — — 1 1 26 13 2.1 1.3 0.2 — — — 1 0.9 27 13 2.1 1.4 1.1 — — — 3.5 0.7 28 13 2.1 1.5 1 — — — 0.2 0.8 29 13 2 1.3 0.9 — — — 0.9 2.5 30 13 2.4 1.5 0.9 — — — 0.8 0.1

TABLE 2 Solidi- Holding Solution Artificial Grain Tensile Elongation Tensile Elongation Impact Speci- fying time after Extru- treatment ageing size strength at strength at Value Density men temp. heating sion temp temp of SI at 20° C. 300° C. at 20° C. 20° C. (J/ (Mg/ No. (° C.) (min) ratio (° C.) (° C.) (μm) (MPa) (%) (MPa) (%) cm²) m³) Example  1 480 60 8 470 200 1.9 105 35 390 10.0 4.5 2.75 of the  2 480 60 8 470 200 2.2 110 31 400 9.5 3.9 2.74 Invention  3 480 60 8 470 200 1.7 120 30 410 6.0 2.7 2.74  4 480 60 8 470 200 1.8 128 28 420 5.5 2.4 2.73  5 480 60 8 470 200 2.5 135 20 432 3.5 2.3 2.72  6 480 60 8 470 200 1.7 105 33 402 5.0 3.8 2.71  7 480 60 8 470 200 1.8 130 28 423 3.7 2.2 2.76  8 480 60 8 470 200 2.2 115 31 410 4.1 3.1 2.74  9 480 60 8 470 200 2.1 125 29 435 3.5 2.1 2.74 10 480 60 8 470 200 2.3 121 31 400 4.5 3.6 2.73 11 480 60 8 470 200 2.6 135 25 441 3.4 2.2 2.72 12 480 60 8 470 200 2.1 131 30 450 3.1 2.5 2.74 13 480 60 8 470 200 2.0 125 27 443 3.3 2.4 2.75 14 480 60 8 470 200 2.1 130 28 440 3.5 2.6 2.73 15 480 60 8 470 200 2.2 110 33 410 7.2 3.1 2.68 16 480 60 8 470 200 1.8 115 29 430 4.5 2.2 2.79 17 480 60 8 470 200 1.7 118 31 405 7.0 3.1 2.74 18 480 60 8 470 200 2.1 120 35 440 3.1 2.1 2.72 Compar- 19 480 60 8 470 200 1.8 65 40 370 13.0 4.9 2.78 ative 20 480 60 8 470 200 2.8 170 15 390 2.4 1.8 2.72 Example 21 480 60 8 470 200 2.1 110 16 430 2.8 1.8 2.75 22 480 60 8 470 200 2.3 100 15 440 1.8 1.7 2.75 23 480 60 8 470 200 2.1 180 12 460 1.9 1.2 2.77 24 480 60 8 470 200 2.0 70 32 380 9.1 5.2 2.70 25 480 60 8 470 200 2.5 135 15 470 1.8 1.5 2.75 26 480 60 8 470 200 1.8 80 35 370 5.5 3.5 2.71 27 480 60 8 470 200 1.9 110 29 430 3.0 2 2.80 28 480 60 8 470 200 2.3 90 36 380 5.0 3.6 2.70 29 480 60 8 470 200 2.2 110 38 460 1.0 0.8 2.70 30 480 60 8 470 200 2.4 105 29 370 7.0 3 2.75

The results in Tables 1 and 2 for Examples No. 1 to No. 5 of the invention and Comparative Examples No. 19 and No. 20 show that by adjusting the content of silicon to not less than 10 mass % and not more than 16 mass %, the material revealed strength and toughness in a balanced manner. Where the content of silicon was over 16 mass %, ductility was not good (Comparative Example No. 20). Where the silicon content was less than 10 mass %, the strength decreased (Comparative Example No. 19).

The results for Examples No. 6 to No. 9 and Comparative Examples No. 21 to No. 24 show that by adjusting the contents of Fe and Ni to ranges of not less than 1 mass % and not more than 3 mass % and not less than 1 mass % and not more than 2 mass %, respectively, the material revealed strength and toughness in a balanced manner. When the Fe content alone or the Ni content alone is increased above the above range in an attempt to improve the heat resistance, coarse intermetallic compounds deposited, thus impairing toughness (Comparative Examples No. 21 and No. 22). When their contents were below the above ranges, heat resistance was impaired. When the material contained both Fe and Ni, if their contents were over the respective ranges, coarse intermetallic compounds deposited, thus impairing toughness (Comparative Example No. 23). When their contents were below the respective ranges, the heat resistance was impaired (Comparative Example No. 24).

The results for Examples No. 10 to No. 14 of the invention and Comparative Examples No. 25 and No. 26 show that by adjusting the content of Ti to not less than 0.5 mass % and not more than 2 mass %, the material revealed strength and toughness in a balanced manner. Similar effects were obtained by adding Zr, Cr, or V in place of Ti. When the total content of these components (Ti, Zr, Cr, V) was over 2 mass %, toughness was impaired (Comparative Example No. 25). When it was less than 0.5 mass %, the strength decreased (Comparative Example No. 26).

The results for Examples No. 15 and No. 16 of the invention and Comparative Examples No. 27 and No. 28 show that by adjusting the content of Cu to not less than 0.6 mass % and not more than 3 mass %, the material revealed strength and toughness in a balanced manner. When the content of Cu was over 3 mass %, the density unduly increased (Comparative Example No. 27), and when it was less than 0.6 mass %, the strength decreased (Comparative Example No. 28).

The results for Examples No. 17 and No. 18 of the invention and Comparative Examples No. 29 and No. 30 show that by adjusting the content of Mg to not less than 0.2 mass % and not more than 2 mass %, the material revealed strength and toughness in a balanced manner. When the content of Mg was over 2 mass %, the toughness decreased (Comparative Example No. 29), and when it was less than 0.2 mass %, the strength decreased (Comparative Example No. 30).

EXAMPLE 2

It was checked how the heating conditions during densification affect the characteristics.

Molten compositions shown in Table 3 were prepared and formed into tensile test specimens and impact test specimens according to the flow of FIG 1. FIGS. 3 and 4 show a tensile test specimen and an impact test specimen, respectively.

For these test specimens, measurements were made of the average grain diameter of the silicon, tensile strength and elongation at 300 degrees C, tensile strength and elongation at room temperature (20 degrees C.), impact value and density. Table 4 shows the results. Table 4 also shows the solidifying temperature of the preform formed into the respective test specimens, holding time after heating the preform, and extrusion ratio, solution treatment temperature, and artificial ageing temperature for the heated preform. TABLE 3 Specimen Content (mass %) No. Si Fe Ni Ti Cr Zr V Cu Mg Example of 31 13 2.1 1.4 0.9 — — — 1.1 0.7 the invention 32 13 2.1 1.4 0.9 — — — 1.1 0.7 33 13 2.1 1.4 0.9 — — — 1.1 0.7 34 13 2.1 1.4 0.9 — — — 1.1 0.7 Comparative 35 13 2.1 1.4 0.9 — — — 1.1 0.7 Example 36 13 2.1 1.4 0.9 — — — 1.1 0.7 Example of 37 13 2.1 1.4 0.9 — — — 1.1 0.7 the invention 34 13 2.1 1.4 0.9 — — — 1.1 0.7 38 13 2.1 1.4 0.9 — — — 1.1 0.7 Comparative 39 13 2.1 1.4 0.9 — — — 1.1 0.7 Example

TABLE 4 Solidi- Holding Solution Artificial Grain Tensile Elongation Tensile Elongation fying time after treatment ageing size strength at strength at Impact Density Specimen temp heating Extrusion temp. temp of Si at 300° C. 300° C. at 20° C. 20° C. value (Mg/ No. (° C.) (min) ratio (° C.) (° C.) (μm) (MPa) (%) (MPa) (%) (J/cm²) m³) (1) 31 400 60 8 390 200 1.5 145 22 420 3.5 2.5 2.74 32 430 60 8 420 200 1.5 130 28 411 4.5 2.7 2.74 33 480 60 8 470 200 1.7 120 30 410 6.0 2.7 2.74 34 510 60 8 500 200 2.5 115 33 403 6.5 3.4 2.74 (2) 35 530 60 8 520 200 4.5 105 20 360 2.4 2.0 2.74 36 380 60 8 370 200 1.4 148 19 430 2.1 1.7 2.74 (1) 37 510 30 8 500 200 1.9 120 32 420 5.7 2.8 2.74 34 510 180 8 500 200 2.5 115 33 403 6.5 3.4 2.74 38 510 270 8 500 200 2.8 100 36 380 6.6 3 2.74 (2) 39 510 330 8 500 200 3.3 85 30 360 4.1 2.5 2.74 (1) Example of the invention (2) Comparative Example

The results in Tables 3 and 4 for Examples No. 31 to No. 34 of the invention and Comparative Examples No. 35 and No. 36 show that by setting the heating and holding temperature of the preform in the solidifying step to a range of 400 degrees C. to 510 degrees C., the material revealed strength and toughness in a balanced manner. When the solidifying temperature was higher than 510 degrees C., not only strength decreased but also the silicon crystals became coarse and functioned as a source of stress concentration, so that ductility decreased (Comparative Example No. 35). When the solidifying temperature was lower than 400 degrees C, strength increased, but toughness was impaired (Comparative Example No. 36).

The results for Examples No. 37 and No. 38 and Comparative Example No. 39 show that by setting the holding time after heating to solidify the preform to not longer than 5 hours, it was possible to prevent the decrease of strength and the decrease of ductility due to coarsening of silicon crystals. When the holding time after heating was longer than 5 hours, both strength and ductility decreased (Comparative Example No. 39).

EXAMPLE 3

The effects of the plastic working method in densification have been examined.

Molten compositions shown in Table 5 were prepared and formed into tensile test specimens and impact test specimens according to the flow of FIG. 1. FIGS. 3 and 4 show a tensile test specimen and an impact test specimen, respectively.

For the test specimens thus prepared, measurements were made of the average grain diameter of the silicon therein, tensile strength and elongation at 300 degrees C., tensile strength and elongation at room temperature (20 degrees C.), impact value and density. Table 6 shows the results. Table 6 also shows the solidifying temperature for the perform in preparing the test specimens, holding time after heating the preform, and extrusion ratio, solution treatment temperature and artificial ageing temperature for the heated preform. TABLE 5 Specimen Content (mass %) No. Si Fe Ni Ti Cr Zr V Cu Mg Example of 40 13 2.1 1.4 0.9 — — — 1.1 0.7 the invention 41 13 2.1 1.4 0.9 — — — 1.1 0.7 42 13 2.1 1.4 0.9 — — — 1.1 0.7 43 13 2.1 1.4 0.9 — — — 1.1 0.7 Comparative 44 13 2.1 1.4 0.9 — — — 1.1 0.7 Example 45 13 2.1 1.4 0.9 — — — 1.1 0.7

TABLE 6 Solidi- Holding Solution Artificial Grain Tensile Elongation Tensile Elongation fying time after treatment ageing size strength at Strength at Impact Specimen temp. heating Extrusion temp. temp. of Si at 300° C. 300 ° C. at 20° C. 20° C. value Density No. (° C.) (min) ratio (° C.) (° C.) (μm) (MPa) (%) (MPa) (%) (J/cm²) (Mg/M³) (1) 40 480 60 6 470 200 1.5 145 30 420 4.5 2.5 2.74 41 480 60 8 470 200 1.5 142 32 425 4.5 2.7 2.74 42 480 60 10 470 200 1.7 144 32 430 5.0 2.7 2.74 43 480 60 12 470 200 1.8 140 35 425 6.5 2.8 2.74 (2) 44 480 60 2 470 200 2.0 105 6 360 0.8 0.5 2.73 45 480 60 4 470 200 1.5 110 8 370 0.9 0.6 2.74 (1) Example of the invention (2) Comparative Example

The results in Tables 5 and 6 for Examples No. 40 to No. 43 of the invention and Comparative Examples Nos. 44 and 45 show that when extrusion is used in the densifying step, by setting the extrusion ratio to not less than 6, the material revealed strength and toughness in a balanced manner. When the extrusion ratio was less than 6, the toughness decreased remarkably (Comparative Examples Nos. 44 and 45).

EXAMPLE 4

The material of Example No. 4 of the invention prepared in Example 1 was subjected to hot plastic working according to the flow of FIG. 2. From the material thus prepared, specimens of shapes shown in FIGS. 3 and 4 were cut out and evaluated to determine their characteristics. The manufacturing conditions and the results of evaluation are shown in Tables 7 and 8. TABLE 7 Specimen Content (mass %) No. Si Fe Ni Ti Cr Zr V Cu Mg Example of 46 13 2.1 1.4 0.9 — — — 1.1 0.7 the invention 47 13 2.1 1.4 0.9 — — — 1.1 0.7 48 13 2.1 1.4 0.9 — — — 1.1 0.7 49 13 2.1 1.4 0.9 — — — 1.1 0.7 Comparative 50 13 2.1 1.4 0.9 — — — 1.1 0.7 Example 51 13 2.1 1.4 0.9 — — — 1.1 0.7

TABLE 8 Holding Heating Artifi- Tensile Im- Solidi- time temp. of Solution cial Grain Tensile Elongation strength Elongation pact Speci- fying after Extru- extruded treatment ageing size strength at at at at value Density men temp heating sion moterial temp. temp of Si 300° C. 300° C. 20° C. 20° C. (J/ (Mg/ No. (° C.) (min) ratio (° C.) (° C.) (° C.) (μm) (MPa) (%) (MPa) (%) cm²) m³) (1) 46 480 60 8 400 470 200 1.8 145 35 420 5.0 3 2.74 47 480 60 8 450 470 200 1.9 142 38 425 5.5 3.5 2.74 48 480 60 8 460 470 200 1.8 141 40 422 6.0 3.3 2.74 49 480 60 8 480 470 200 2.0 135 42 420 6.5 3.2 2.74 (2) 50 480 60 8 500 490 200 4.5 95 25 380 4.0 2.8 2.74 51 480 60 8 520 500 200 6.4 90 18 370 3.0 2 2.74 (1) Example of the invention (2) Comparative Example

The results for Examples No. 46 to No. 49 of the invention and Comparative examples Nos. 50 and 51 show that among the characteristics of the materials obtained by hot plastic working at a higher temperature than the solidifying temperature for the extruded material, both strength and ductility decreased (comparative examples Nos. 50 and 51).

All the embodiments and examples disclosed herein should be considered to be not restrictive but exemplary in all respects. The scope of the present invention should be defined not by the above description but by the claims and includes all and any modifications falling in the meanings and scope of the claims.

INDUSTRIAL APPLICABILITY

The heat-resistant, high-toughness aluminum alloys according to the present invention are advantageously used as materials for automotive engine parts for which heat resistance and toughness are required, particularly as materials for pistons. 

1. A heat-resistant, high-toughness aluminum alloy comprising not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum, said alloy being obtained by densifying aluminum alloy powder prepared by gas atomizing, said silicon having an average grain diameter of not more than 4 μm.
 2. The heat-resistant, high-toughness aluminum alloy of claim 1 which contains titanium by not less than 0.5 mass % and not more than 2 mass %.
 3. The heat-resistant, high-toughness aluminum alloy of claim 1 or 2 having a density of 2.8 Mg/m³ or less.
 4. An engine part manufactured by subjecting the heat-resistant, high-toughness aluminum alloy of any of claims 1 to 3 to hot plastic working.
 5. The engine part of claim 4 which is a piston.
 6. A method of manufacturing a heat-resistant, high-toughness aluminum alloy comprising: preparing aluminum alloy powder by gas atomizing, said aluminum alloy powder comprising not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum; subjecting said aluminum alloy powder to cold forming to obtain a preform; heating said preform to a temperature range of not less than 400 degrees C. and not more than 510 degrees C. and holding said preform in said temperature range for 5 hours or less; and subjecting said preform to hot plastic working to densify said preform, thereby obtaining a dense body as said heat-resistant, high-toughness aluminum alloy; the silicon in said aluminum alloy having an average grain diameter of 4 μm or less.
 7. A method of manufacturing a heat-resistant, high-toughness aluminum alloy comprising: preparing aluminum alloy powder by gas atomizing, said aluminum alloy powder comprising not less than 10 mass % and not more than 16 mass % of silicon, not less than 1 mass % and not more than 3 mass % of iron, not less than 1 mass % and not more than 2 mass % of nickel, not less than 0.5 mass % and not more than 2 mass % in total of one or more selected from the group consisting of titanium, zirconium, chromium and vanadium, not less than 0.6 mass % and not more than 3 mass % of copper, and not less than 0.2 mass % and not more than 2 mass % of magnesium, the balance being essentially aluminum; subjecting said aluminum alloy powder to cold forming to obtain a preform; heating said preform to a temperature range of 400 degrees C. to 510 degrees C. and holding said preform in said temperature range for 5 hours or less; subjecting said preform to hot plastic working to densify said preform, thereby obtaining a dense body; and subjecting said dense body to hot plastic working by heating to a temperature not higher than the heating temperature of said preform, thereby manufacturing said aluminum alloy; the silicon in said aluminum alloy having an average grain diameter of 4 μm or less.
 8. The method of claim 6 or 7 wherein the step of subjecting said preform to hot plastic working includes extruding with an extrusion ratio of 6 or more. 